Puricare s approach to Brackish Water Irrigation and Saline Soils During dry summer months many farmers experience serious problems with the increased salinity of irrigation water due to more intensive irrigation, surface evaporation of river water and the addition of dissolved salts to irrigation water originating from mines and salty fertilizers. The high salt concentration has an adverse effect on the water s infiltration capability and also on the physical condition of the soil - but photosynthesis is also limited due to the formation of salt deposits/precipitate on leaf surfaces and the development of burnt symptoms. The suitability of water for irrigation purposes depends on the concentration and types of salts (especially Sodium salts) present in the water. Irrigation water containing high Sodium concentrations can still be useful if the Calcium (Ca) and Magnesium (Mg) concentrations are also high. The concept of Sodium Adsorption Ratio (SAR) was developed to express the relationship of the Sodium concentration as a ratio to the total Calcium and Magnesium concentrations. Once the SAR value exceeds 12 up to 15, severe soil structure problems develop and plants experience difficulty to absorb water. Puricare and irrigation with brackish water: The Puricare Agricultural Unit releases activated oxygen into irrigation water that cleans the irrigation systems, reacts with minerals such as Calcium Carbonate (CaCO 3 ) and increases its solubility, results in a better Sodium Adsorption Ration (SAR) and improves the adverse salt effects of the water. Puricare s water treatment does not remove the excess Sodium and Chloride ions in the water, but can improve their harmful effects through the increased solubility of minerals (e.g. Calcium Carbonate/CaCO 3 ) and the increased assimilation of Ca and Mg by plants.
Salt deposits of untreated brackish Soutneerslag water van on onbehandelde a clover leaf The treated brackish water did not form salt deposits on the clover leaves Water that has been treated by the unit no longer forms salt deposits on the leaves, no burnt symptoms can be observed and the leaves can photosynthesize successfully. Salty/Saline soils: Improper irrigation practices, poor soil management, inadequate internal soil drainage and increased surface evaporation during drought conditions allow salts to accumulate and soils to become unproductive. In general, soils with high salt concentrations are referred to as salty/saline soils. Three different types of saline soils are distinguished, namely: saline soil, sodium saline soil and sodic soil. 1. Saline soil has a high concentration of neutral salts (not sodium salts), the saturation extract has an electrical conductivity (EC) higher than 400 millisiemens (ms) per meter, an ESP (Exchangeable Sodium Percentage) and SAR lower than 15 and a ph lower than 8.5. Saline soils are recognizable by a white layer of dry salt on the soil surface. These salts are usually chlorides or sulphates of Ca, Mg en Na. 2. Sodium saline soils contain both a high salt and sodium content, the electrical conductivity of the saturation extract is higher than 400 ms, 1 m the UNP and SAR are higher than 15 and the ph is below 8.5. 3. Sodic soils do not have a high salt content, but a high exchangeable sodium content. The electrical conductivity of the saturation extract is lower than 400 ms, 1 m the SAR and UNP are higher than 15 and the ph is above 8.5.
A high concentration of soluble sodium salts in soil increases the osmotic pressure of the soil solution causing plants to absorb water and nutrients with difficulty. Plants may experience drought whilst in relatively wet soil. The monovalent Na + ions have large hydrated ion diameters and an abundance of exchangeable Na + ions causes the electric double layer to thicken, the clay colloids to repel each other and to become dispersed as separate particles. In structured soils the dispersion causes the bonds between the clay particles to weaken, the aggregates to break up, soil structure and macro porosity to deteriorate and the pores to shrink due to the thick electrical double layer. This results in a very low effective pore volume through which water can flow freely and hence a low saturated hydraulic conductivity. Sodic soils are characterized by a low infiltration rate, they are poorly aerated, and crust formation and compaction of the top layer occur. The high ph of sodium soils is the result of a high concentration of Na2CO3 in the soil which hydrolyses to OH ions. Na2CO3 + 2H2O --------2 Na + + 2OH + H2CO3 The high ph causes humus to dissolve and to form a black precipitate on soil surfaces, hence the common name of black brack soils. The abnormal high ph also affects the accessibility of other elements. The improvement of saline/brackish soil: To improve saline soil is not a simple process with a quick or easy solution. New scientific management practices are locally not as well known as in Israel, the Middle East and Australia. There, irrigation, transpiration and plant water requirements are carefully measured and compared with soil types and drainage capacity. The only real successful method in South Africa to improve saline conditions comprises the leaching of very saline soils.
The main aim should be to remove (to leach) salts from the root zone because of the high sensitivity of the hair roots to excessive salts. Sodium is a very mobile element because of the high solubility of all Sodium salts and because Sodium ions are relatively poorly adsorbed by soil colloids. Leaching of excess salts is a time consuming procedure and if the drainage is not professionally done, the soil s fertility can be destroyed. This is especially a problem in low-laying fields along the river, or where the groundwater is very shallow and leaching is not below the root level of the plant (300 to 900mm). When the groundwater table rises (e.g. following rain or irrigation in the absence of proper drainage), the salty groundwater may reach the upper soil layers and, thus, supply salts to the root zone. Thus, the improvement of saline soils includes, essentially, leaching and a subsurface drainage system. Saline soils are usually easily recovered by repeated leaching with water, but the recovery of sodic soils is difficult because of the fairly permanent physical damage and the low saturated hydraulic conductivity. Recovery is only possible by repeatedly mixing large quantities of gypsum (calcium sulfate / CaSO 4. 2H 2 O) with the soil so the Ca ++ ions can replace the exchangeable Na + ions after which the sodium salts are gradually washed out from the soil profile with irrigation water of good quality (containing a low concentration of harmful salts). When the excess Na + ions are removed, the dominant exchangeable cations are di- and trivalent (e.g. Ca ++ ) with small hydrated ion diameters, the electrical double layer is thin and the clay particles stick together to form larger units. This condition, called Flocculation, promotes structure formation and maintenance of the macro porosity of soil. It is a laborious and expensive process and if the natural internal drainage of the soil is poor, the installation of an artificial subsurface drainage system is essential. Puricare s contribution to the improvement of saline soils: The Puricare Agricultural Unit aims to rehabilitate poor agricultural soils and also to improve saline soils. The activated oxygen in irrigation water reacts with minerals such as Calcium Carbonate (CaCO 3 ), increases its solubility, results in a better Sodium Adsorption Ratio (SAR)
and together with higher oxygen levels in the soil, it improves aeration, water infiltration and root system development to ensure healthy crop growth. Sound agricultural practices (e.g. the application of gypsum/s-containing fertilizers/organic material) followed by repeated irrigation with treated water can leach out excessive salts (e.g. as Na2SO4) from the soil profile. Dispersed clay is systematically flocculated, favorable conditions are created for structure formation and water retaining capacity and soil quality are improved. Compiled by: